I noticed today a much larger number of bees flying around the entrance of my hive than are usually present. I mean a LOT more. At most times, there are maybe 10 - 20 bees visible, coming and going through the entrance. Now, there appear to be 100 or more flying around in front of the hive and competing to get in/out.

I did recently (within the last month) requeen the hive and all seemed to be good. New queen accepted. Brood being laid. Could this be just the results of having a healthier, egg laying queen and the new workers now emerging and foraging? Or, is this possibly swarming behavior? Or something else?

We’ve also recently experienced a pretty sudden transition from summer weather into fall… a few days of rain and cooler temperatures (lows in the 50’s (F) and highs in the upper 60’s) after a relatively dry and warm summer.

It could be a result of a better laying queen laying more brood and newly emerged bees doing orientation flights about the hive. That would account for extra activity about the hive so I doubt you have anything to worry about especially if the old queen was failing. If the bees were out foraging they would fly away from the hive but when the bees a circling the hive look at it as orientation flights.
Cheers